Unix Internal

What is Unix Internals on a Layman's Language.Can I consider
Unix Internal expert for a Unix's Position?

Thanks

UNIX Internals expertise is detailed C system programming experience at the system call interface level and lower in the kernel. If you have a lot of expertise at C programming with these system calls you will be all set to go!

Hi ,
send me if know some links of Unix unternals such as thread programming , mutex , etc.

you can try,

Unix Internals book by Maurice J. Bach